The invention described herein relates to high explosives and more particularly to thermally-stable, plastic-bonded explosives.
New requirements for high explosives have appeared in many applications of modern ordnance. In particular, there are various modern ordnance applications that require the explosive to see extended service at elevated temperatures. Accordingly, explosive compositions having a reasonable explosive performance and a high degree of thermal stability are desired. Additionally, such a heat-resistant explosive should be capable of being readily formed into the varied shapes required in modern ordnance and should have a sufficient strength to retain its structural integrity under rather severe thermal conditions.
Plastic-bonded explosives represent a class of explosives which can be made into pressings from which can be fabricated--usually by machining--desired shapes. These explosives are pressed from so-called molding powders which are typically prepared by the slurry technique. Powdered explosive and water are mixed in a kettle equipped with a condenser and agitator. A lacquer composed of the plastic (together with a plasticizer, if necessary) dissolved in a suitable solvent is added to the slurry. The solvent is removed by distillation, causing the plastic phase to precipitate out on the explosive. The plastic-explosive agglomerates into "beads" as the stirring and solvent removal continues. Finally, water is removed from the beads by filtration and drying; the resultant product is the molding powder. The powder is then pressed into shape by either compression molding with steel dies or hydrostatic or isostatic pressing under vacuum. The pressing may readily be machined into a desired shape for actual use.
Plastic-bonded, HMX-based explosives normally use energetic binder systems, such as nitroaliphatic compounds or nitrate esters, to maximize their explosive power. High-density, halogenated resins are also used for this purpose. Unfortunately, both of these binder types introduce problems. The thermal stability of energetic binder materials is less than that of the HMX filler. This property limits the service life of the explosive in high temperature applications. Although the halogenated resin binders are thermally stable, they are undesirable in that they cause the explosive to be unduly sensitive in the skid test, an important measure of handling safety.